Field
Integrated circuit devices.
Description of Related Art
High access resistance has been one of the limiters for realizing high performance germanium (Ge) NMOS devices. One contributor to the high access resistance is the high Schottky barrier height (SBH) of metal/n+Ge contact. The Fermi level tends to be pinned near the valence band for most metals/Ge contacts. Such pinning is beneficial for PMOS devices but a disadvantage for NMOS devices. In addition, it is generally more difficult to achieve high n-type dopant concentration in germanium and then in silicon.